In 2006, there were over 11.4 million cancer survivors in the US. However for many individuals with cancer, improved survival is complicated by long-term behavioral effects including depression. Indeed, the prevalence of depression in breast cancer survivors is nearly three to five times greater than the general population. Yet, the unique clinical, behavioral, and biological factors that prospectively contribute to increased depression risk in breast cancer survivors is not known. In older adults, we have found that sleep disturbance independently contributes to depression occurrence, and this prospective risk is specific to those with a history of depression. Breast cancer status may add to that risk, as we have found that breast cancer survivors with insomnia have a prevalence of depression history that is nearly twice that in older women with insomnia; yet, other factors in the prior risk model do not generalize to breast cancer survivors. There are no published prospective data that have examined the independent contribution of sleep disturbance on depression occurrence in breast cancer survivors. Increasing evidence also implicates sleep disturbance in the activation of inflammatory signaling, which serves as a biological mechanism that contributes to depression. Hence, in this SEER-affiliated tumor registry-based study, we will evaluate 300 early stage-, older adult (>55 years) breast cancer survivors and 300 age-matched comparison women, stratified by a history of major depression. All participants will be community members of Kaiser Permanente Southern California (KPSC), a large nonprofit health plan that serves over 3 million members. In a prospective cohort study, older adult breast cancer survivors vs. comparisons, stratified by depression history will be evaluated at baseline (i.e., 1 year post- primary treatmen for breast cancer survivors) and at 6, 12, 18, and 24 months with the following aims: 1) to determine the prospective association between sleep disturbance and depression occurrence; 2) to evaluate the prospective association between sleep disturbance and cellular and genomic markers of inflammation; and 3) to examine the prospective relationships between sleep disturbance, cellular and genomic markers of inflammation, and depression occurrence. Understanding the cancer-specific clinical, behavioral, and biological factors that prospectively contribute to depression risk in breast cancer survivors vs. comparison older women will substantially alter clinical management by leading to the development of a targeted intervention for depression prevention, specific for breast cancer survivors. PUBLIC HEALTH RELEVANCE: Sleep disturbance is one of the most frequent complaints in breast cancer survivors. Sleep disturbance is hypothesized to be associated with increases of inflammation and depression occurrence. This study will examine the prospective relationships between sleep disturbance, inflammation, and depression occurrence in older adult breast cancer survivors vs. comparison women. Findings will inform the development of cancer-specific treatments that target disordered sleep and/or inflammation for prevention of depression in breast cancer survivors.